The invention relates to the recovery of purified agarose from agar or agarose using a lower alkylene glycol.
Agarose is a neutral galactose polysaccharide obtained from agar. Agar also contains agaropectin, a sulfated polysaccharide considered to be undesirable when present in agarose. Because agarose contains no charged groups, aqueous agarose gels are employed as a medium for electrophoresis and in immunodiffusion.
Several methods are reported in the literature for recovering agarose from agar. U.S. Pat. No. 3,281,409 issued to Blethen is a commercially-used process that uses carrageenan and a quaternary ammonium salt to precipitate the agaropectin component from an agar-containing solution. U.S. Pat. No. 3,362,884 issued to Morse selectively separates the agaropectin from agar by degrading the agaropectin with pectinase to render it water soluble. Even though these procedures selectively remove agaropectin from the agar, the additives used in the separation procedure can remain behind in the agarose-containing fraction as impurities.
This drawback is minimized in the agarose recovery method described by Polson in U.S. Pat. No. 3,335,127, which employs polyethylene glycol to fractionate a purified agarose product from agarose/agaropectin mixtures. Polyethylene glycol is contacted with an aqueous solution containing the impure agarose at elevated temperature to precipitate the purified agarose product. Since water-soluble impurities like color bodies tend to coprecipitate with the agarose in a one pass procedure, the Polson fractionation procedure must be repeated to obtain a high purity product.
The present invention also fractionates a purified agarose product but employs low molecular weight alkylene glycols in a procedure that differs from the approach utilized in Polson's method. In contrast to Polson's use of polyethylene glycol to induce precipitation of agarose from an aqueous agarose solution, the present invention first dissolves the impure agarose into the lower alkylene glycol, and the desired agarose product is thereafter precipitated from the agarose/glycol solution.
Because most impurities remain behind in the glycol in the present invention, the recovered agarose product is exceptionally pure. Another characteristic provided by the present invention is that the recovered agarose product readily dissolves in aqueous solution, without resort to high solution temperatures.